Superheterodyne receiver



1933- K. POSTHUMUS ET AL SUPERHETERODYNE RECEIVER Filed Jan. 5, 1932 INVENTORS KLAAS PO$THUMU5 THEODORUS J.WEYER5 BY g g r M ATTORNEY Patented Oct. 17, 1933 UNITED STATES 1,930,691" SUPERHETERODYNE RECEIVER Klaas Posthumus and Theodorus Josephus Wey ers, Eindhoven,

Netherlands, assignors to Radio Corporation of America; a corporation of Delaware Application January 5, 1932, Serial No. 584,784, and in Germany J une 23, 1931 6 Claims (Cl. 250' The present invention relates to improvements in, or relating to, superheterodyne receivers.

In the case of superheterodyne receivers the oscillator circuit must be tuned to a frequency 5 which differs by a constant amount afrom the frequency p of the station which-it is desired to receive. Consequently, the frequency of the oscillator circuit must be pic. Inthis case the frequency a is that to which the mean or intermediate frequency amplifier following the first detector has. to be permanently tuned selectively. If a further station operates simultaneously on a frequency pi2a, the waves of this reflection station or image frequency after interference with the oscillator waves also pass through the mean frequency amplifier, except when care is taken that these undesired waves cannot interfere with the oscillator oscillations. According to the present invention. this result is obtained by inserting in the aerial circuit a by-path, or by-pass, constituting a short circuit for the frequency'of the reflection station and adapted to be tuned to this frequency so that the tuning is effected automatically and in a constrained manner by the adjustment of the main tuningamember or the main tuning members on the station to bereceived According to the present invention, for this purpose preferably use is made of the circuit arrangement known per se in which two circuits are tuned by means of identical and mechanical.- ly coupled condensers, and in which the inductances of the said circuits are different from each other, and one of these circuits includes a large series and a small parallel condenseix, This arrangement ensures that the two last mentioned condensers and the difference in induction of the two circuits are such that for, any positions of the coupled condensers the tunings of the two circuits have a substantially constant difference in frequency.

In order that the invention may be clearly understood and readily carried into effect,- two embodiments thereof will now be described more fully, by way of example, with reference to the accompanying drawing, in which:

Fig. 1 shows a circuit arrangement in which in addition to the short-circuit path for the waves of the reflection station use is made of means of selection in the aerial circuit of the superheterodyne receiver.

Fig. 2 shows a circuit arrangement devoid of such means of selection. 1

In the circuit arrangement shown in Fig. 1, a receiver antenna 1 is connected to earth or ground through a fixed condenser 2' of high capacity, a coil 3 and a variable condenser 4. The latter has connected in parallel to it a small fixed condenser 5. A second variable condenser are connected between the antenna 1 which is also connected to the control grid of a high frequency tube 8 and the earth. The values of the coils 3 and 7 are chosen so as to be slightly different, and the two fixed condensers 2 and 5 are so proportioned that for any identical positions of the condensers 4 and 6 the tunings of the series circuit 2, 3, 4, 5, and of the fly-wheel circuit 6, '7, have a, substantially constant difference equal to double the mean frequency a, Consequently, when the circuit 6, 7 is tuned to the frequency p of the station to be received, the circuit 2, 3, 4, 5, constitutes at the same time a short-circuit path for the reflection frequency pi2a. a

The anode circuit of the tube 8 includes a coil 9 and in parallel therewith a fixed condenser 15 connected'in series with a variablecondenser 10. Said circuit is tuned to the frequency p, and is coupled to the grid circuit of theoscillator valve 18 by means of the condenser 15. This grid circuit includes a coil 14 the, inductance of which is different from that of the coil 9. The coil 14 has connected in parallel therewith a fixed large condenser 11, a variable condenser 12 and a condenser 15, which are mutually connected in series, and a small fixed condenser 13 is connected in parallel with the condenser 12'.

By properly proportioning these various values it is possible to ensure that if the variable condensers 10 and 12 are equal there is in any positions of these condensers a substantially constant difference a between the frequenciesto which the circuits 9, 10, 15 and 11, 12, 13, 15, 14 respectively are tuned. The tube 18 is brought to self-oscillation by the fact that its anode circuit includes .a coil 19 which is inductively coupled to the coil 14, A blocking condenser 16 keeps the anode voltage aloof from the control grid, and a leakage resistance 17 ensures that the proper mean potential of said grid is maintained,

Owing to the fact that the two tuning circuits mentioned before are coupled by the condenser l5 beat oscillations of the frequency. a

are set up which are sifted out by the first detector ,23 whose circuit 24 is tuned to thesaid frequency. The control grid ,of this detector is isolated from theanode voltage by a blocking condenser 20, and is maintained on the negative voltage necessary for anode detection by a leakage resistance 21 and a battery 22.

The further amplification of the mean frequency oscillations and the detection and amplification of the signal with which. the oscillation is modulated are effected in a manner known per se. The circuit arrangement shown in Fig. 2 is only different from that shown in Fig. 1 in that the primary tuning circuit 6, 7 is replaced by a resistance 25. I

The consequent risk of a so-called cross modulation can be avoided by the use of tubes having a so-called variable amplification factor.

While we have indicated and described several systems for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of our invention as set forth in the appended claims.

What is claimed is:. s

1. A radio receiver including a tuning network consisting of at least two resonant circuits,

one of said circuits including a coil and a variable tuning condenser in series, said condenser being adapted to tune the coil through a range of undesired frequencies, the other circuit including a coil, and a variable tuning condenser, the ratio of the inductance values of said coils being other than unity and the second condenser being of the same type as the first condenser, said second condenser being adapted to tune the second resonant circuit through a range of desired signal frequencies, means for simultaneously adjusting both condensers, and means for maintaining the frequency difference between said circuits a constant throughout said ranges, said means comprising a relatively large capacity and a relatively small capacity connected respectively in series and in parallel with one of the condensers.

'2. A radio receiver including a tuning network consisting of at least two resonant circuits, one of said circuits including a coil and a variable tuning condenser in series, said condenser being adapted to tune the coil through a range of undesired frequencies, the other circuit including a coil and a variable tuning condenser, the ratio of the inductance values of said coils being other than unity and the second condenser being of the same type as the first condenser, said second condenser being adapted to tune the second resonant circuit through a range of desired signal frequencies, means for simultaneously adjusting both condensers, and means for maintaining the frequency difference between said circuits a con- "stant throughout said ranges, said means comprising a relatively large capacity and a relatively small capacity connected respectively in series and in parallel with one of the condensers, one of the variable condensers being connected -in shunt with the coil of its resonant circuit, and the other condenser being connected in series with the coil of its resonant circuit.

3. A radio receiver including a tuning network consisting of at least two resonant circuits, one of said circuits including a coil and a variable tuning condenser in series, said condenser ,being adapted to tune the coil through a range -of undesired frequencies, the other circuit including a coil and a variable tuning condenser, the ratio of the inductance values of said coils being other than unity and the second condenser being of the same type as the first condenser, said second condenser being adapted to tune-the second resonant circuit through a range of desired signal frequencies, means for simultaneously adjusting both condensers, and means for maintaining the frequency difference between said circuits a constant throughout said ranges, said means comprising a relatively large capacity and a relatively small capacity connected respectively in series and in parallel with one of the condensers and an electron discharge tube coupling said resonant circuits.

.4. A radio receiver including a tuning network consisting of at least two resonant circuits, one of said circuits including a coil and a variable tuning condenser in series, said condenser being adapted to tune the coil through a range of undesired frequencies, the other circuit including a coil and a variable tuning condenser, the ratio of the inductance values of said coils being other than unity and the second condenser being of the same type as the first condenser,

said second condenser being adapted to tune the second resonant circuit through a range of desired signal frequencies, means for simultaneously adjusting both condensers, and means for maintaining the frequency difference between said circuits a constant throughout said ranges, said means comprising a relatively large capacity and a relatively small capacity connected .respectively in series and in parallel with one of the condensers, an electron discharge tube, and both said circuits being connected across the input electrodes of the tube.

'5. A radio receiver including a tuning network consisting of at least two resonantcircuits, one of said circuits including a coil and a variable tuningcondenser in series, said condenser being adapted to tune the coil'through a range of undesired frequencies, the other circuit in-' cluding a coil and a variable tuning condenser, the ratio of the inductance values of said coils being other than unity and the second condenser being of the same type as the first condenser, said second condenser being adapted to tune the second .resonantcircuit through a range of desired signal frequencies, means for simultaneously adjusting both condensers, and means for maintaining the frequency difference between said circuits .a constant throughout said ranges, said means comprising a relatively large capacity and a relatively small capacity connected respectively in series and in parallel with one of the condensers, a source of local oscillations including a resonant circuit provided with a coil and a variablecondenser adapted to tune it over a range of oscillation frequencies differing from said desired signal range by a desired .beat frequency, means for coupling the second and third .resonant circuits, said last variablecondenser being arranged for simultaneous adjustment with said first two condensers, and means in said third resonant circuit for maintaining said beat frequency constant throughout adjustment of said three condensers.

6. In a superheterodyne receiver, an oscillator stage including a resonant input network, said .network including a pair of parallel resonant paths, one of the paths including a coil and a variable tuning condenserin series, the second path consisting 'of a coil and a similar condenser in' shunt, means for uni-control of both condensers, the first path being tunable through a range .of undesired signal image frequencies ,and thesecond path .being tunable through arange of desired signal frequencies, and a capacity=in shunt withsaid series tuning condenser and a capacity in serieswith the latter for constantly maintaining the frequency difference between said two ,paths throughout said ranges equal to twice'the intermediate frequency of the receiver.

KLAASPOSTHUMUS.

THEODORUS JOSEPI-IUS WEYERS. 

